PROTHENA PLC (PRTA)
Health Care · Biotechnology · NASDAQ
A clinical-stage biotech developing antibody therapies targeting misfolded proteins in Parkinson's disease, Alzheimer's disease, and rare amyloidosis through proprietary CYTOPE® intracellular delivery technology, in partnership with major pharma.
What PROTHENA PLC does
Prothena is a late-stage clinical biotechnology company focused on the discovery and development of novel therapies for diseases caused by protein dysregulation. Its pipeline addresses neurodegenerative and rare peripheral amyloid diseases, including Parkinson’s disease, Alzheimer’s disease, ATTR amyloidosis with cardiomyopathy, and amyotrophic lateral sclerosis (ALS). The company utilizes a proprietary CYTOPE technology platform to target intracellular disease pathways and advances its therapeutic candidates primarily through strategic partnerships with large pharmaceutical companies.
Themes: Parkinson's disease / synucleinopathies, ATTR amyloidosis, Alzheimer's disease, Amyotrophic lateral sclerosis (ALS), Protein misfolding / amyloid diseases, CNS / neurodegeneration, Monoclonal antibodies, Cell-internalizing delivery technology
Fundamentals
- Price$9.45 as of 2026-08-21 close
- Market cap$485M as of 2026-08-21
- 1-year return+10.4% 2025-08-21 close $8.56 → 2026-08-21 close $9.45
- P/En/a negative earnings
- Net margin-80.7% as of 2026-08-24
- ROE-15.0% as of 2026-08-24
- Debt / equity0.00 as of 2026-08-24
- Revenue growth (YoY)-92.8% FY2025 vs FY2024, SEC XBRL
- Revenue CAGR (3y)-43.6% SEC XBRL
- Beta-0.33 as of 2026-08-24
- Last reported earnings2026-08-06 SEC EDGAR Form 8-K (Item 2.02)
How PRTA compares in its sector
- net profit marginmiddle range 504 covered Health Care peers, as of 2026-08-24
- operating marginmiddle range 504 covered Health Care peers, as of 2026-08-24
- return on equitymiddle range 576 covered Health Care peers, as of 2026-08-24
- 3-year revenue CAGRbottom 10% 402 covered Health Care peers
Position among covered Health Care companies that report each metric (minimum 5 peers). A relative position within our covered catalog — not a valuation, quality, or investment judgment. A higher percentile is simply a higher value (for P/E, more expensive on earnings — never "better"). Informational only.
How PROTHENA PLC looks technically
PROTHENA PLC (PRTA) is trading 1.1% below its 200-day average, the long-term trend line — a long-term downtrend. Its 50-day average crossed below its 200-day average about 32 trading days ago — a "death cross", a bearish long-term signal. There is no clear trend right now — the price is choppy (ADX, a 0–100 trend-strength gauge, is 13, below the 25 that marks a real trend). Momentum is neutral — its 14-day RSI (a 0–100 momentum gauge) is 59, neither overbought (above 70) nor oversold (below 30). It just made a new 20-day high, its first since 2026-07-09, pushing above its recent trading range. It is 19.9% below its highest point of the past year.
Trend
7
| Distance from the 200-day | it is trading 1.1% below its 200-day average, the long-term trend line — a long-term downtrend | -1.1% |
|---|---|---|
| 50-day moving average | its average price over the last 50 trading days — a short-term trend line — is $8.94 | $8.94 |
| 200-day moving average | its average price over the last 200 trading days — the long-term trend line — is $9.56 | $9.56 |
| Swing structure | its recent peaks and dips disagree — one of them is rising while the other is not, so there is no clean up or down pattern in the swings | mixed — one of the two is not confirming |
| Last swing turn | its last significant turn was a swing high 8 calendar days ago — the swings before that are what the structure reading is measured on | 8 sessions |
| Since the 50/200 cross | its 50-day average crossed below its 200-day average about 32 trading days ago — a "death cross", a bearish long-term signal | 32 sessions |
| Trend strength (14-day ADX) | there is no clear trend right now — the price is choppy (ADX, a 0–100 trend-strength gauge, is 13, below the 25 that marks a real trend) | 12.7 |
Momentum
3
| 14-day RSI | momentum is neutral — its 14-day RSI (a 0–100 momentum gauge) is 59, neither overbought (above 70) nor oversold (below 30) | 59.5 |
|---|---|---|
| Position in its 14-day range | it is trading right at the top of its 14-day range ($8.06 to $9.52) — its "stochastic" reading is 95 out of 100, where 0 would mean closing exactly at the 14-session low and 100 exactly at the high. This measures WHERE the price sits inside its recent range, which is a different question from the RSI beside it: RSI is a momentum gauge, measuring how FAST the price has been moving, so a stock can drift quietly to the bottom of its range with an ordinary RSI, or fall sharply and still sit in the middle. It has been climbing within that range over the last few sessions. | 95.2 |
| Since the MACD crossed zero | MACD, a trend-momentum gauge, is in positive territory (momentum leaning bullish) | 12 sessions |
Range
12
| 52-week high | its highest closing price over the past year (about 252 trading days) was $11.80 | $11.80 |
|---|---|---|
| From the 52-week high | it is 19.9% below its 52-week high (its highest price of the past year) | -19.9% |
| Above the 52-week low | it is 22.3% above its 52-week low (its lowest price of the past year) | +22.3% |
| Below the 52-week high | it is 19.9% below its highest point of the past year | 19.9% |
| Since a 20-day breakout | it just made a new 20-day high, its first since 2026-07-09, pushing above its recent trading range | 1 session |
| Since a 55-day breakout | it made a new 55-day low about 16 trading days ago | 16 sessions |
| All-time high | its highest closing price on record is $79.75 (set on 2021-09-27) | $79.75 |
| Given back of the 52-week move | over the past year its closes ranged ($8.06 to $11.51), and it has given back a bit over half of its rise from last year’s low — 60% of it. Chart-watchers call 61.8%-65% given back the "golden pocket" — for this company that is $9.27 to $9.38. It is watched widely enough that orders cluster there, which is the honest reason it matters; it is not a forecast. | 59.7% |
| From the all-time high | it is 88.2% below its all-time high | -88.2% |
| Nearest price level | it is trading 2.3% below a resistance level at $9.67 — a price it turned at four times since 2025-10-17, most recently on 2026-02-20. Since 2024-08-21 it has 4 such levels below the current price and 11 above. Levels like these describe where the price has reversed or paused before; they are not a forecast of where it will go. | +2.3% |
| All-time low | its lowest closing price on record is $4.32 (set on 2025-05-28) | $4.32 |
| Above the all-time low | it is 118.7% above its all-time low | +118.8% |
Volatility
5
| Band width vs its own 6 months | day-to-day price swings are about average versus its own recent 6-month history | 31st percentile |
|---|---|---|
| Typical daily range | in a typical session it travels about $0.4384 between its high and its low — about 4.6% of its price. That is its "average true range" over the last 14 sessions, which also counts the distance from the previous close, so a day that opens well away from yesterday counts as the large move it was | $0.4384 |
| Bollinger bands (20-day, ±2σ) | most of its recent trading has stayed between about $8.09 and $9.50 — the "Bollinger bands", a range drawn two standard deviations either side of its 20-day average price, which widens when the stock gets more volatile and narrows when it settles | $8.09 – $8.80 – $9.50 |
| Typical daily range (% of price) | its price moves about 4.6% in a typical session — about typical for the companies we cover. This is the average gap between a session's high and low over the last 14 sessions, counting overnight moves, expressed against the current price so it can be compared with companies trading at any price | 4.6% |
| Stretch from the 200-day average | it is trading 0.3 daily ranges below its 200-day average price (1.1% below it in plain percentage terms) — a way of asking how far it has stretched from its own average in units of how far it normally moves in a day, so a calm company and a jumpy one can be compared on the same scale | 0.3 daily ranges below its 200-day average |
Volume
1
| Volume vs its 30-day average | trading volume is about normal versus its 30-day average | 0.75× |
|---|
Analyst
2
| Change in the average price target | analysts' average price target is unchanged from the prior reading | 0.0% |
|---|---|---|
| Change in the consensus rating | the analyst consensus rating is unchanged since the prior reading | unchanged |
Candlestick patterns
2
| Since a hammer | 1 session ago, after a stretch of decline, it sold off hard during the session and then closed back near its high — a "hammer", the long lower wick showing the drop was bought back before the close | 1 session ago |
|---|---|---|
| Since a bearish engulfing | 3 sessions ago it opened above the previous session's close and finished below that session's open — a "bearish engulfing" pair, where one down day more than undid the up day before it | 3 sessions ago |
Price gaps
3
| Gap at the open | it opened on 2026-08-21 0.9% above the previous session's close — an overnight gap, the part of the move that happened while the market was shut, and had not traded back through that level by the close | +0.9% |
|---|---|---|
| Open gap | it gapped 2.3% above the previous close 2 sessions ago and has not traded back through the level it left behind at 8.71 — an "unfilled gap", which describes a price range no trade has since crossed and is not a forecast that it will be crossed | +2.3% |
| Gap filled | a 2.0% gap down opened on 2026-07-23 has been "filled" 21 sessions ago — price traded back through the level the gap left behind, and it closed again during the very session that opened it | 21 sessions ago |
Price streaks
1
| Closing streak | it closed higher in its latest session, after a session that did not close higher — a single up day rather than a run | 1 session up |
|---|
Relative strength
4
| vs market, 1 month | over the past 1 month this stock beat the market by 5.7 percentage points (the stock gained 8.0% while the market gained 2.3%) | +5.7% |
|---|---|---|
| vs market, 3 months | over the past 3 months this stock lagged the market by 2.7 percentage points (the stock gained 0.4% while the market gained 3.1%) | -2.7% |
| vs market, 6 months | over the past 6 months this stock lagged the market by 6.3 percentage points (the stock gained 4.8% while the market gained 11.1%) | -6.3% |
| vs market, 12 months | over the past 12 months this stock lagged the market by 10.1 percentage points (the stock gained 10.4% while the market gained 20.5%) | -10.1% |
Signal agreement
2
| Bullish technical signals | 2 of the 9 technical signals we can compute for it are currently in a bullish state: a fresh 20-day high, MACD momentum is positive — these describe past price behaviour, not a forecast | 2 of 9 |
|---|---|---|
| Bearish technical signals | 4 of the 9 technical signals we can compute for it are currently in a bearish state: a "death cross" — its 50-day average is below its 200-day, trading below its 200-day average, lagging the market over 6 months, near the top of its 14-day range (overbought) — these describe past price behaviour, not a forecast | 4 of 9 |
Trend (Ichimoku cloud)
1
| Vs the Ichimoku cloud | trading inside the Ichimoku cloud — a band drawn from where its own highs and lows sat up to 2026-07-16 and projected forward over today's price, the zone traders read as unresolved — neither side has established a trend, and the band is where that gets settled. The band itself is thick, spanning 8.2% of the share price, which is taken to mean a barrier that has held for a while and takes effort to cross. | 0.0% |
|---|
Volume-weighted price
2
| Vs this year’s average price paid | the price is 1% above the average price paid so far this year, so the typical buyer over that stretch is showing a gain. That average is $9.36 — a volume-weighted average of daily closes over 158 sessions, not a true tick-by-tick VWAP. | +0.9% |
|---|---|---|
| Vs the average paid since it last reported | the price is 5% above the average price paid since it last reported on 2026-08-06 (its 10-Q), so the typical buyer over that stretch is showing a gain. That average is $9.03 — a volume-weighted average of daily closes over 12 sessions, not a true tick-by-tick VWAP. | +4.7% |
Price levels it has turned at before
PRTA last closed at $9.45 on 2026-08-21. Since 2024-08-21 it has turned at 4 prices below its last close and 11 above; the 3 nearest below and the 3 nearest above are listed, nearest first.
| Level | Side | Distance | Evidence |
|---|---|---|---|
| $9.67 | Resistance | 2.3% above the last close | turned there four times · 2025-10-17 to 2026-02-20 |
| $9.04 | Support | 4.3% below the last close | turned there five times · 2025-04-21 to 2026-07-27 |
| $10.18 | Resistance | 7.7% above the last close | turned there five times · 2025-04-23 to 2026-07-02 |
| $8.63 | Support | 8.6% below the last close | turned there twice · 2025-09-08 to 2026-01-12 |
| $10.46 | Resistance | 10.7% above the last close | turned there twice · 2026-01-23 to 2026-04-24 |
| $8.21 | Support | 13.1% below the last close | turned there twice · 2026-02-05 to 2026-02-20 |
A level is a price this company reversed or paused at more than once — they describe past behaviour, not a forecast of where the price will go.
Wave structure
No Elliott-wave labelling currently fits its swings: the recent highs and lows do not satisfy the three rules a five-wave count has to obey, so there is no count to show rather than a count we are unsure about.
Read from daily closes as of 2026-08-21.
An Elliott-wave count describes the swings already printed and the level that would disprove it. It is not a forecast, a target, or advice.
Screens: Trading below the 200-day moving average · Broke out to a new 20-day high · trendless / choppy (low ADX) · lagging the market · At the top of its 14-day range (stochastic above 80) · Near the golden pocket (has given back about two thirds of its 52-week move) | Learn: moving average · golden cross · adx · rsi · breakout · fifty two week high low
Based on daily closing prices as of 2026-08-21. Describes past price behavior only — informational, not financial advice.
Analyst consensus
- Consensus ratingBuy (2.50 mean, 1=Strong Buy…5=Strong Sell) — 5 analysts
- Mean price target$21.40 range $8.00 – $36.00; median $20.00
Analyst estimates, as of 2026-08-23. These are third-party analyst opinions and price targets, aggregated — not a recommendation, prediction, or advice from stocks-llm. Informational only.
Analyst EPS estimate for PRTA
- Consensus EPS estimate-$0.38 next reporting period, as of 2026-08-23
Change over time is not available yet: it needs two readings of the same reporting period at least 30 days apart, and we have been recording these estimates since 2026-08-04. An estimate for a DIFFERENT quarter is not a revision, so a reading from before the last report is never compared with one after it.
The consensus estimate for the next reporting period, and how it has moved between readings of that SAME period. A change is measured only between readings estimating one period — when a company reports, the consensus moves to the next quarter and the two numbers are not comparable. Informational only, not a forecast and not advice.
Key risks (from latest filing)
["Clinical development failure risk — most programs are in Phase 2-3 trials with uncertain regulatory approval; prasinezumab Phase 3 trial results critical to valuation","Dependence on major pharma partnerships — primary revenue and development success rely on Roche, Novo Nordisk, and Bristol Myers Squibb; partnership terminations or setbacks would significantly impact financials","Severe unprofitability and cash burn — company is deeply unprofitable (net margin -260.92%) with declining revenue (-57.99% YoY), creating ongoing funding and runway risks"]
What changed in the latest 10-Q
AI-assisted comparison of PRTA's 10-Q filed 2026-05-07 against the prior one filed 2025-11-06.
Management's Discussion & Analysis (MD&A)
- Added:
- Newer filing adds section on Overview that includes: 'The Company's pipeline includes both wholly-owned and partnered programs being developed for the potential treatment of diseases including Parkinson's disease, ATTR amyloidosis with cardiomyopathy, Alzheimer's disease, Amyotrophic lateral sclerosis (ALS) and a number of other neurodegenerative diseases.'
- Newer filing adds: 'Prothena is developing and applying CYTOPE ® a novel technology that incorporates a cell-internalizing domain to drive efficient cytosolic delivery with highly specific marcomolecular effectors.'
- Newer filing adds detailed scientific background section on α-synuclein protein function, misfolding, genetic evidence, and cell-to-cell transmission mechanisms
- Newer filing states: 'In the fourth quarter of 2025, Roche initiated the Phase 3 PARAISO clinical trial' (actual initiation date)
- Newer filing adds: 'In March 2026, Roche presented an analysis from the ongoing PADOVA open-label extension (OLE) study at the International Conference on Alzheimer's and Par' (text truncated)
- Removed:
- Older filing's Overview section containing specific details about BMS partnerships (BMS-986446/PRX005 for Alzheimer's disease and PRX019) is removed in newer filing
- Older filing's reference to 'Our wholly-owned and unpartnered portfolio includes clinical and preclinical-stage programs that we are exploring strategic interest to further develop' is removed
- Older filing's statement about Novo Nordisk share purchase agreement and ATTR amyloidosis business (coramitug/PRX004) milestone payments is removed
- Older filing's June 2025 announcement that 'Roche announced that it will advance prasinezumab into Phase 3 development and plans to initiate the Phase 3 PARAISO clinical trial... by the end of 2025' is removed
- Older filing's April 2025 reference to 'results from the Phase 2b PADOVA trial were presented for the first time in an oral presentation by Roche at the International Conference on Alzheimer's and Parkinson's Diseases' is removed
- Older filing's statement about 'Positive trends towards reduced motor progression at 104 weeks (two years) were observed, showing 30-40% relative reduction versus placebo' is removed
- Older filing's statement that 'The PADOVA study also provided the first biomarker evidence of prasinezumab impacting the underlying disease biology' is removed
- Older filing's references to PASADENA Phase 2 trial results and early-start group analysis are removed
- Reworded:
- Form 10-K date reference changed from 'February 27, 2025 (the "2024 Form 10-K")' in older filing to 'February 27, 2026 (the "2025 Form 10-K")' in newer filing
- Phase 3 PARAISO primary endpoint wording changed from 'with a timeframe of at least 104 weeks' to 'at a minimum of 104 weeks'
- Clinical trial description changed from future tense ('plans to initiate') to past tense ('Roche initiated')
- Notes:
- Newer filing text appears truncated at end of PADOVA section, limiting full comparison of that subsection
- Older filing text also appears truncated at end, limiting full historical comparison
Risk Factors
- Added:
- Reference to 2025 Form 10-K filed February 27, 2026 (newer filing references 2025 annual report vs. older filing's 2024 annual report)
- Net income of $32.7 million for three months ended March 31, 2026
- Net loss of $244.1 million for year ended December 31, 2025
- Accumulated deficit of $1.3 billion as of March 31, 2026
- Cash and cash equivalents of $329.5 million as of March 31, 2026
- Reference to Phase 1 clinical trial for PRX019 in wind-down activities
- Removed:
- Reference to 2024 Form 10-K filed February 27, 2025
- Net losses of $222.5 million for nine months ended September 30, 2025
- Net loss of $116.9 million for year ended December 31, 2022
- Accumulated deficit reference dated September 30, 2025
- Cash and cash equivalents of $330.8 million as of September 30, 2025
- Reference to 'wind down the Phase 1 clinical trials for PRX012 and Phase 3 clinical trial for birtamimab'
- Reference to 'Phase 2 and 2b clinical trials for prasinezumab being conducted by Roche'
- Reference to 'Amended Distribution Agreement (as may be further amended from time to time)'
- Reworded:
- Updated from 'nine months ended September 30, 2025' to 'three months ended March 31, 2026' for interim period reporting
- Changed from listing 2024, 2023, and 2022 losses to listing 2025, 2024, and 2023 losses
- Removed phrase 'and Phase 3 clinical trial for birtamimab' from wind-down activities description
- Simplified clinical trial description for prasinezumab from 'Phase 2 and 2b clinical trials' to 'Phase 3 clinical trial'
- Removed reference to 'Amended Distribution Agreement' in equity financing discussion
- Notes:
- Text is truncated at end of both documents, limiting full comparison of complete section
- Changes primarily reflect updated quarterly reporting period and current financial metrics rather than material risk disclosure changes
AI-assisted comparison of two SEC filing sections. It describes wording and theme changes only, makes no materiality, legal, or investment judgement, and is not financial advice. Informational only — not financial advice.
Insider activity (SEC Form 4)
6 open-market purchases and 2 open-market sales by insiders in the last 90 days.
- Last 30 days2 buys ($323220) · 2 sells ($135975) — 1 buying, 2 selling insiders
- Last 90 days6 buys ($2M) · 2 sells ($135975) — 1 buying, 2 selling insiders
- Last 180 days7 buys ($3M) · 2 sells ($135975) — 1 buying, 2 selling insiders
Activity heuristic: net buying (a transparent product heuristic from the counts above, not a prediction or advice)
Most recent open-market transaction: 2026-08-07. As of 2026-08-24.
View full insider trading history → View SEC Form 3/4/5 filingsAsk about PRTA's insider activity →
Only open-market purchases (SEC code P) and sales (code S) are counted here. Option exercises, vesting/awards, gifts, and shares withheld for taxes are excluded — they are compensation or mechanical, not open-market conviction. Sales may be planned and non-discretionary (e.g. a Rule 10b5-1 plan) and are not necessarily bearish; open-market buying is not a recommendation to buy. Informational only — not financial advice.
Short interest (FINRA)
PRTA had 8,172,438 shares of reported short interest as of the 2026-07-31 FINRA settlement date (delayed, bi-monthly; not real-time).
PRTA had 15.9% of its shares outstanding sold short as of the 2026-07-31 FINRA settlement date (percent of FLOAT would be higher — float is not disclosed in the source). FINRA reported 13.96 days to cover at the same settlement.
- Reported short interest (shares) 8,172,438
- Short interest (% of shares outstanding) 15.9%
- Prior settlement (shares) 8,196,964
- Reported change -0.3%
- Days to cover (reported) 13.96
Reported to FINRA as of the 2026-07-31 settlement date. Short interest is reported to FINRA and published on a delayed, bi-monthly schedule (as of a settlement date, disseminated roughly eight business days later) — it is NOT real-time, does not cover every venue or all US trading, and is not a short-squeeze prediction or investment advice. Days-to-cover is the value FINRA reports; percent of float is not shown because the source file carries no share-count denominator — where a percent appears it is of shares OUTSTANDING, the larger base, and is therefore a floor on percent of float. Informational only — not financial advice.
Competitors & peers
AI-enriched competitor set. Linked names are companies covered by stocks-llm; other named peers are shown for reference only.
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Frequently asked questions
What does PROTHENA PLC (PRTA) do?
Prothena is a late-stage clinical biotechnology company focused on the discovery and development of novel therapies for diseases caused by protein dysregulation. Its pipeline addresses neurodegenerative and rare peripheral amyloid diseases, including Parkinson’s disease, Alzheimer’s disease, ATTR amyloidosis with cardiomyopathy, and amyotrophic lateral sclerosis (ALS).
What sector is PROTHENA PLC (PRTA) in?
PROTHENA PLC (PRTA) is classified in the Health Care sector. Its industry is Biotechnology. It trades on NASDAQ.
Who are PROTHENA PLC's (PRTA) competitors?
Notable peers of PROTHENA PLC (PRTA) include Roche, Novo Nordisk, Bristol Myers Squibb, Biogen and Eli Lilly. This peer set is informational only — not financial advice.
Is PROTHENA PLC (PRTA) overbought or oversold right now?
PROTHENA PLC (PRTA) is currently neither overbought nor oversold — its 14-day RSI (a 0–100 momentum gauge) is 59, in the neutral middle (as of 2026-08-21). RSI describes recent price momentum, not a forecast — informational only, not financial advice.
Where does stocks-llm's data on PRTA come from?
Fundamentals and prices come from market data, as of 2026-08-24; company filings and profile facts come from SEC EDGAR. All figures are delayed daily-close data shown with their as-of date — informational only, not financial advice.
Fundamentals: market data, as of 2026-08-24. Filings: SEC EDGAR. Prices are delayed daily-close data.
Last updated 2026-08-21.
Informational only — NOT financial advice. All figures are delayed daily-close data from SEC EDGAR & market data, shown with their as-of date.