PROTHENA PLC (PRTA)
Health Care · Biotechnology · NASDAQ
Prothena is a clinical-stage biotechnology company developing novel therapies for protein dysregulation diseases like Alzheimer's and Parkinson's through a collaborative, partner-focused model.
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, particularly neurodegenerative and rare peripheral amyloid diseases. The company leverages its proprietary CYTOPE technology to target intracellular disease pathways and develops a pipeline of therapeutic candidates often through strategic partnerships with major pharmaceutical companies.
Recent developments
The company updated its full-year 2026 cash guidance to approximately $259 million (midpoint) following second quarter results. Results from the Phase 2b PADOVA trial for prasinezumab (partnered with Roche) were published in The Lancet, and multiple research collaborations for the CYTOPE technology are ongoing.
From PROTHENA PLC's filing of 2026-08-06.
Themes: neurodegenerative diseases, protein dysregulation, amyloidosis, Alzheimer's disease, Parkinson's disease, ALS, intracellular drug delivery
Fundamentals
- Price$8.61 as of 2026-10-08 close
- Market cap$442M as of 2026-07-30 (share count; price 2026-10-08)
- 1-year return-16.8% 2025-10-08 close $10.35 → 2026-10-08 close $8.61
- P/En/a negative earnings
- Net margin-2520.6% FY2025, SEC XBRL
- ROE-87.0% FY2025, SEC XBRL
- Debt / equity0.00 as of 2026-09-02
- Revenue growth (YoY)-92.8% FY2025 vs FY2024, SEC XBRL
- Revenue CAGR (3y)-43.6% SEC XBRL
- Beta0.77 as of 2026-09-02
- Last reported earnings2026-08-06 SEC EDGAR Form 8-K (Item 2.02)
How PRTA compares in its sector
- net profit marginbottom 10% 430 covered Health Care peers, as of 2026-09-02
- operating marginbottom 10% 417 covered Health Care peers, as of 2026-09-02
- return on equitybottom 25% 510 covered Health Care peers, as of 2026-09-02
- 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 7.5% 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 65 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 14, below the 25 that marks a real trend). Momentum is neutral — its 14-day RSI (a 0–100 momentum gauge) is 49, neither overbought (above 70) nor oversold (below 30). MACD, a trend-momentum gauge, turned bullish about 1 trading day ago (its momentum flipped positive). It made a new 20-day low about 3 trading days ago. It is 27.0% below its highest point of the past year. Day-to-day price swings are unusually narrow versus its own recent history — a "Bollinger squeeze" (in the tightest 8% of the past ~6 months), which often precedes a bigger move.
Trend
8
| Distance from the 200-day | it is trading 7.5% below its 200-day average, the long-term trend line — a long-term downtrend | -7.5% |
|---|---|---|
| 50-day moving average | its average price over the last 50 trading days — a short-term trend line — is $8.86 | $8.86 |
| 200-day moving average | its average price over the last 200 trading days — the long-term trend line — is $9.31 | $9.31 |
| Swing structure | each recent peak has been lower than the one before it and each dip deeper — the pattern chart-watchers call a downtrend, which describes where price has already been and not where it goes next | lower highs and lower lows |
| Last swing turn | its last significant turn was a swing high 16 calendar days ago — the swings before that are what the structure reading is measured on | 16 sessions |
| Wave structure | its recent swings can be read as a five-part downward sequence — what Elliott-wave chartists call an impulse — now in leg 3 of five; the labelling fails if price closes above 9.09. It is one of several labellings that fit, and it describes the swings already printed, not what comes next. The same swings also read as a three-part correction in leg C. | possible downward five-wave sequence, in wave 3 (one of several readings) |
| Since the 50/200 cross | its 50-day average crossed below its 200-day average about 65 trading days ago — a "death cross", a bearish long-term signal | 65 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 14, below the 25 that marks a real trend) | 14.4 |
Momentum
3
| 14-day RSI | momentum is neutral — its 14-day RSI (a 0–100 momentum gauge) is 49, neither overbought (above 70) nor oversold (below 30) | 49.3 |
|---|---|---|
| Position in its 14-day range | it is trading in the upper half of its 14-day range ($7.80 to $9.09) — its "stochastic" reading is 63 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. | 62.8 |
| Since the MACD crossed zero | MACD, a trend-momentum gauge, turned bullish about 1 trading day ago (its momentum flipped positive) | 1 session |
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 27.0% below its 52-week high (its highest price of the past year) | -27.0% |
| Above the 52-week low | it is 11.4% above its 52-week low (its lowest price of the past year) | +11.4% |
| Below the 52-week high | it is 27.0% below its highest point of the past year | 27.0% |
| Since a 20-day breakout | it made a new 20-day low about 3 trading days ago | 3 sessions |
| Since a 55-day breakout | it made a new 55-day low about 3 trading days ago | 3 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 ($8.02 to $11.51), and it has recovered roughly a quarter of its fall from last year’s high — 17% of it. Chart-watchers call 61.8%-65% given back the "golden pocket" — for this company that is $10.18 to $10.29. It is watched widely enough that orders cluster there, which is the honest reason it matters; it is not a forecast. | 16.9% |
| From the all-time high | it is 89.2% below its all-time high | -89.2% |
| Nearest price level | it is sitting right on a resistance level at $8.62 — a price it turned at three times since 2025-09-08, most recently on 2026-08-18. Since 2024-10-08 it has 2 such levels below the current price and 10 above. Levels like these describe where the price has reversed or paused before; they are not a forecast of where it will go. | +0.1% |
| 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 99.3% above its all-time low | +99.3% |
Volatility
5
| Band width vs its own 6 months | day-to-day price swings are unusually narrow versus its own recent history — a "Bollinger squeeze" (in the tightest 8% of the past ~6 months), which often precedes a bigger move | 8th percentile |
|---|---|---|
| Typical daily range | in a typical session it travels about $0.4295 between its high and its low — about 5.0% 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 | $0.4295 |
| Bollinger bands (20-day, ±2σ) | most of its recent trading has stayed between about $8.02 and $9.01 — 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 | $8.02 – $8.52 – $9.01 |
| Typical daily range (% of price) | its price moves about 5.0% 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 | 5.0% |
| Stretch from the 200-day average | it is trading 1.6 daily ranges below its 200-day average price (7.5% 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 | 1.6 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 | 1.36× |
|---|
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 | not available for this company yet | n/a |
Candlestick patterns
4
| Since a doji | 5 sessions ago it opened and closed at almost the same price after trading through a wider range — a "doji", the classic picture of buyers and sellers finishing the session level | 5 sessions ago |
|---|---|---|
| Since a hammer | 3 sessions 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 | 3 sessions ago |
| Since a bullish engulfing | 1 session ago it opened below the previous session's close and finished above that session's open — a "bullish engulfing" pair, where one up day more than undid the down day before it | 1 session ago |
| Since a bearish engulfing | 6 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 | 6 sessions ago |
Price gaps
3
| Gap at the open | it opened on 2026-10-08 0.6% below the previous session's close — an overnight gap, the part of the move that happened while the market was shut, and traded back through that level before the close | -0.6% |
|---|---|---|
| Open gap | it gapped 2.2% below the previous close 22 sessions ago and has not traded back through the level it left behind at 9.82 — an "unfilled gap", which describes a price range no trade has since crossed and is not a forecast that it will be crossed | -2.2% |
| Gap filled | a 2.3% gap up opened on 2026-09-30 has been "filled" 6 sessions ago — price traded back through the level the gap left behind, and it closed again during the very session that opened it | 6 sessions ago |
Price streaks
1
| Closing streak | it has closed higher 2 sessions in a row, a +7.36% move over the run — an unbroken run of up days, which describes what has already happened and says nothing about the next session | 2 sessions up |
|---|
Relative strength
4
| vs market, 1 month | over the past 1 month this stock lagged the market by 10.8 percentage points (the stock lost 9.7% while the market gained 1.0%) | -10.8% |
|---|---|---|
| vs market, 3 months | over the past 3 months this stock lagged the market by 16.4 percentage points (the stock lost 12.6% while the market gained 3.8%) | -16.4% |
| vs market, 6 months | over the past 6 months this stock lagged the market by 31.7 percentage points (the stock lost 14.2% while the market gained 17.5%) | -31.7% |
| vs market, 12 months | over the past 12 months this stock lagged the market by 31.8 percentage points (the stock lost 16.8% while the market gained 15.0%) | -31.8% |
Signal agreement
2
| Bullish technical signals | 1 of the 9 technical signals we can compute for it is currently in a bullish state: MACD momentum is positive — these describe past price behaviour, not a forecast | 1 of 9 |
|---|---|---|
| Bearish technical signals | 5 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, a fresh 20-day low, lagging the market over 6 months, trading below the Ichimoku cloud — these describe past price behaviour, not a forecast | 5 of 9 |
Trend (Ichimoku cloud)
1
| Vs the Ichimoku cloud | trading 5.2% below the Ichimoku cloud — a band drawn from where its own highs and lows sat up to 2026-09-01 and projected forward over today's price, the side traders read as an established downtrend, with the band above acting as the level that would have to be cleared. The band itself is thin, spanning 0.2% of the share price, which is taken to mean a barrier that gives way easily. | -5.2% |
|---|
Volume-weighted price
2
| Vs this year’s average price paid | the price is 7% below the average price paid so far this year, so the typical buyer over that stretch is under water. That average is $9.27 — a volume-weighted average of daily closes over 191 sessions, not a true tick-by-tick VWAP. | -7.1% |
|---|---|---|
| Vs the average paid since it last reported | the price is 2% below the average price paid since it last reported on 2026-08-06 (its 10-Q), so the typical buyer over that stretch is under water. That average is $8.82 — a volume-weighted average of daily closes over 45 sessions, not a true tick-by-tick VWAP. | -2.4% |
Descending triangle, either side — broke down · the lower entry $8.23 · 89 sessions in
Price levels it has turned at before
PRTA last closed at $8.61 on 2026-10-08. Since 2024-10-08 it has turned at 2 prices below its last close and 10 above; the 2 nearest below and the 3 nearest above are listed, nearest first.
| Level | Side | Distance | Evidence |
|---|---|---|---|
| $8.62 | Resistance | 0.1% above the last close | turned there three times · 2025-09-08 to 2026-08-18 |
| $8.21 | Support | 4.7% below the last close | turned there three times · 2026-02-05 to 2026-09-16 |
| $9.04 | Resistance | 5.0% above the last close | turned there 7 times · 2025-04-21 to 2026-09-30 |
| $8.04 | Support | 6.7% below the last close | turned there four times · 2025-08-28 to 2026-07-31 |
| $9.67 | Resistance | 12.3% above the last close | turned there four times · 2025-10-17 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
Its recent swings can be read as a five-part downward sequence — what Elliott-wave chartists call an impulse — now in leg 3 of five.
This labelling fails — stops being a possible reading at all — if it closes above $9.09.
This is one of several labellings that fit the same swings, so treat it as a reading rather than the reading. It was chosen from 2 labellings that survived the rules, counting shorter readings of the same bars.
On past moves of this shape the leg has usually ended somewhere between $6.39 and $7.42 — that is where it has tended to end if the count holds, not a forecast of where the price goes.
Alternate reading: The same swings also read as a three-part correction in leg C, which fails on a close above $9.09.
This reading has stood for 8 trading days, since 2026-09-29.
Read from daily closes as of 2026-10-08.
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 · Pulled back from the 12-month high · Broke down to a new 20-day low · MACD just crossed bullish (12/26/9) · in a Bollinger Band volatility squeeze · trendless / choppy (low ADX) | Learn: moving average · golden cross · adx · rsi · macd · breakout · fifty two week high low · bollinger bands
Based on daily closing prices as of 2026-10-08. Describes past price behavior only — informational, not financial advice.
Analyst consensus
- Mean price target$21.40 range $8.00 – $36.00; median $20.00
Analyst estimates, as of 2026-10-04. 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 2026-10-04
- Estimate change, 30 days$0.00 from -$0.38, on 2026-08-30, 35-day window
- Readings revised upward0% of 7 comparable readings
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)
["Significant history of operating losses and uncertainty regarding future profitability.","Requirement for substantial additional capital to fund clinical trials and long-term research operations.","Heavy reliance on strategic partnerships with large pharmaceutical companies for the advancement and commercialization of key clinical programs."]
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.
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)
8 open-market purchases and 2 open-market sales by insiders in the last 90 days, of which we have read Form 4 filings through 2026-10-04. The 5 days since 2026-10-04 have not been checked yet.
- Last 30 days · read to 2026-10-044 buys ($4M) · 0 sells — 1 buying insider
- Last 90 days · read to 2026-10-048 buys ($5M) · 2 sells ($135975) — 1 buying, 2 selling insiders
- Last 180 days · read to 2026-10-0413 buys ($8M) · 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: 2026-10-02. Based on Form 4 filings read through 2026-10-04; anything filed since is not yet included.
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 8,544,664 shares of reported short interest as of the 2026-09-15 FINRA settlement date (delayed, bi-monthly; not real-time).
PRTA had 16.6% of its shares outstanding sold short as of the 2026-09-15 FINRA settlement date (percent of FLOAT would be higher — float is not disclosed in the source). FINRA reported 26.53 days to cover at the same settlement.
- Reported short interest (shares) 8,544,664
- Short interest (% of shares outstanding) 16.6%
- Prior settlement (shares) 8,495,796
- Reported change 0.58%
- Days to cover (reported) 26.53
Reported to FINRA as of the 2026-09-15 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
- Roche (RHHBY)
- Novo Nordisk (NVO)
- Bristol Myers Squibb (BMY)
- Biogen (BIIB)
- Eli Lilly (LLY)
- Acadia Pharmaceuticals (ACAD)
- Alnylam Pharmaceuticals (ALNY)
AI-enriched competitor set. Linked names are companies covered by stocks-llm; other named peers are shown for reference only.
Compare PRTA vs…
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, particularly neurodegenerative and rare peripheral amyloid diseases. The company leverages its proprietary CYTOPE technology to target intracellular disease pathways and develops a pipeline of therapeutic candidates often through strategic partnerships with major pharmaceutical companies.
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 49, in the neutral middle (as of 2026-10-08). RSI describes recent price momentum, not a forecast — informational only, not financial advice.
Where does stocks-llm's data on PRTA come from?
Fundamentals come from SEC XBRL company filings for the figures marked with a fiscal year, and market data, as of 2026-09-02 for the rest; prices are market data, as of 2026-09-02; 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: SEC XBRL company filings for the figures marked with a fiscal year, and market data, as of 2026-09-02 for the rest. Filings: SEC EDGAR. Prices are delayed daily-close data.
Last updated 2026-10-08.
Informational only — NOT financial advice. All figures are delayed daily-close data from SEC EDGAR & market data, shown with their as-of date.