Simulations Plus, Inc. (SLP)

Simulations Plus, Inc. was founded in 1996 by Walter Woltosz and is headquartered in Lancaster, California, in the Antelope Valley north of Los Angeles. The company began as a developer of software for predicting how pharmaceutical compounds behave in the body, and it grew into a provider of modeling and simulation tools used in drug discovery and development. Woltosz had previously founded Words+, an assistive-communication technology company, before turning to pharmaceutical science software.

Its flagship product, GastroPlus, simulates the absorption, distribution and pharmacokinetics of drugs in humans and animals. The software portfolio also included ADMET Predictor, which estimates molecular properties from chemical structure, along with DDDPlus, MembranePlus and MedChem Designer. Customers included pharmaceutical and biotechnology companies, as well as agrochemical, cosmetics and food firms, academic groups and regulatory agencies. Revenue came primarily from annual software licenses.

The company broadened its offerings through acquisitions. It bought Cognigen Corporation in 2014, adding clinical pharmacology consulting and creating a services segment alongside software. The 2017 purchase of DILIsym Services brought quantitative systems toxicology models such as DILIsym, NAFLDsym and later additions covering other organ systems. Further deals added the Lixoft modeling platform in 2020 and Immunetrics, a quantitative systems pharmacology business, in 2022. The company reported results in two segments, Software and Services.

Simulations Plus traded on the Nasdaq Stock Market under the symbol SLP after earlier trading on the NYSE American exchange, and it was a small-cap company in the life sciences tools sector. In later years it faced slower growth, particularly in its services business, and leadership changes as Woltosz stepped back from day-to-day management. The company also dealt with softer demand from biotechnology customers during a period of tighter funding in the sector.

In 2026 Simulations Plus agreed to be acquired by affiliates of Altaris, LLC, a private equity firm focused on healthcare investments. The agreement valued the company at roughly $377 million and provided $18.50 in cash for each outstanding share. The parties announced the expiration of the Hart-Scott-Rodino antitrust waiting period before the closing, and the company later issued an announcement regarding a change in the acquisition status.

The merger was completed on October 6, 2026, and Simulations Plus became a privately held company owned by Altaris affiliates. A Form 25 was filed on the same day to remove the common stock from listing and registration on Nasdaq, and the company began the process of ending its SEC reporting obligations. Shareholders received the cash consideration, and the SLP ticker ceased to trade.

Simulations Plus was regarded as a long-standing example of model-informed drug development, an approach that regulators such as the U.S. Food and Drug Administration have increasingly accepted in submissions. Its software was used to support decisions on dosing, formulation and drug interaction risk before and during clinical trials. With the take-private, the company's products and services continue under private ownership, while public shareholders no longer hold stock in the business.