Stocks › Drug Manufacturers - Specialty & Generic › AMPH

Amphastar Pharmaceuticals AMPH

US equityMarket cap rank #3187Drug Manufacturers - Specialty & Generic Cannabis & Hemp

$25.54 −$0.37 (-1.43%)

Market closed · Oct 8, 7:20 am ET · Last extended-hours $25.54 0.00%

Open$25.91

Prev close$25.91

Day range$25.29 – $26.17

Volume776.3K

Market cap$1.09B

P/E (TTM)15.1

Dividend yield–

Ownership & positioning

Who holds it, who is betting against it, and where the big money is moving

Institutional ownership84.1%+0.17 pts vs. prior quarter

Institutions holding266+1 vs. prior quarter

Insider trades (recent)23 buys / 27 sellsNet selling

Short interest11.74% of floatDays to cover 10.8 · as of 15 Sep 2026

Short-sale volume share22.3%5-day average of daily volume

Short-sale volume as % of daily volume

Large-order net flow, last 20 sessions

Net of large-order buying minus selling, in USD. Over this window: −$662.9K (10 inflow days, 10 outflow days).

Net flow by order size, last 20 sessions

Super/Big orders approximate institutional-size trades; Mid/Small approximate retail-size trades. Net buy minus sell value in each bucket, summed over the window.

The five largest holders on file together own 44.0% of shares outstanding.

Largest holders

Applied Physics & Chemistry Laboratories, Inc.16.05%
BlackRock12.28%
Yongfeng Zhang6.28%
Dimensional Fund Advisors5.42%
Vanguard Capital Management, LLC4.01%
State Street Global Advisors3.86%
American Century Investment Management2.77%
Ziping Luo2.62%

By investor type

Mutual Fund53.97%
Private Company17.94%
Individual/Insider10.36%
Hedge Fund8.05%
Public Company2.31%
Government Pension Fund1.17%
Family Office/Trust0.39%
Insurance Company0.24%

Reported short interest has risen from 8.72% to 11.74% of float over the last 6 biweekly reports (30 Jun 2026 to 15 Sep 2026).

Recent institutional activity

Holder	Type	Period	Share change	New stake
Nuveen Asset Management LLC	Insurance Company	2026/Q3	+72,728	0.2%
Hudson River Trading LLC	Private Company	2026/Q3	+331,349	0.9%
Dimensional Fund Advisors	Mutual Fund	2026/Q3	+277,160	5.4%
D. E. Shaw & Co., L.P.	Hedge Fund	2026/Q3	+221,506	2.1%
American Century Investment Management	Mutual Fund	2026/Q3	+159,088	2.8%
AQR Capital Management	Hedge Fund	2026/Q3	+128,285	0.5%
Two Sigma Investments, LP	Hedge Fund	2026/Q3	+109,967	0.6%
Denali Advisors, LLC	Mutual Fund	2026/Q3	+109,500	0.9%
The Goldman Sachs Group, Inc.	Public Company	2026/Q3	+101,270	0.8%
First Trust Advisors L.P.	Mutual Fund	2026/Q3	+96,360	0.6%
Jane Street Group, LLC	Private Company	2026/Q3	+86,259	0.4%
Goldman Sachs Asset Management, L.P.	Mutual Fund	2026/Q3	+74,702	0.4%
Algert Global LLC	Hedge Fund	2026/Q3	+69,040	0.3%
Leap Investments LP	Mutual Fund	2026/Q3	+56,700	0.1%
O'Shaughnessy Asset Management, LLC	Mutual Fund	2026/Q3	+55,498	0.4%

Institutional buy/sell activity by reporting period, largest moves first.

Insider transactions

Date	Insider	Title	Transaction	Shares	Price	Held after
20 Sep 2026	William Peters	CFO, Executive VP of Finance, Treasurer & Director	Automatic Disposition	-4,139	$25.00	66,753
15 Sep 2026	Rong Zhou	Senior Executive Vice President of Production	Derivative Exercise and Sale	-10,000	$23.94	205,877
1 Sep 2026	Rong Zhou	Senior Executive Vice President of Production	Open Market Disposition	-3,187	$23.63	205,877
31 Aug 2026	Rong Zhou	Senior Executive Vice President of Production	Intent to Sell (Form 144)	-13,187	$22.00	–
10 Aug 2026	Richard Prins	Lead Independent Director	Open Market Disposition	-7,973	$20.30	21,482
6 Aug 2026	William Peters	CFO, Executive VP of Finance, Treasurer & Director	Automatic Disposition	-3,127	$22.48	70,892
6 Aug 2026	William Peters	CFO, Executive VP of Finance, Treasurer & Director	Derivative Exercise and Sale	-5,053	$22.48	70,892
8 Jul 2026	Anthony Pierce	Independent Director	Other Acquisition	+7,886	–	7,886
8 Jul 2026	Anthony Pierce	Independent Director	Other Derivative Acquisition	+16,646	$19.02	16,646
1 Jun 2026	Shiren S. Lee	Independent Director	Sale to Issuer	-769	$18.45	151,207
31 May 2026	Michael Zasloff	Independent Director	Other Acquisition	+8,143	–	13,265
31 May 2026	Michael Zasloff	Independent Director	Other Derivative Acquisition	+17,365	$18.42	17,365
31 May 2026	Richard Prins	Lead Independent Director	Other Acquisition	+8,143	–	13,265
31 May 2026	Richard Prins	Lead Independent Director	Other Derivative Acquisition	+17,365	$18.42	17,365
31 May 2026	Shiren S. Lee	Independent Director	Other Acquisition	+8,143	–	8,143
31 May 2026	Shiren S. Lee	Independent Director	Other Derivative Acquisition	+17,365	$18.42	17,365
31 May 2026	Gayle Deflin	Independent Director	Other Acquisition	+8,143	–	13,265
31 May 2026	Gayle Deflin	Independent Director	Other Derivative Acquisition	+17,365	$18.42	17,365
31 May 2026	David Gaugh	Director	Other Acquisition	+8,143	–	14,447
31 May 2026	David Gaugh	Director	Other Derivative Acquisition	+17,365	$18.42	17,365

From Form 4/Form 144 filings. Negative share counts are disposals (sales, gifts, or shares withheld for taxes); positive are acquisitions.

Short interest, by report

Report date	Shares short	% of float	Days to cover
15 Sep 2026	4,994,808	11.7%	10.8
31 Aug 2026	5,134,473	12.1%	15.4
14 Aug 2026	5,385,239	12.7%	10.0
31 Jul 2026	4,928,331	11.2%	11.9
15 Jul 2026	4,174,460	9.5%	11.2
30 Jun 2026	3,845,576	8.7%	5.2

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