(Bloomberg) -- Two more pharmaceutical companies are having difficulty supplying Adderall to US patients with attention-deficit/hyperactivity disorder as shortages plague the market.

Lannett Co. and Par Pharmaceuticals, part of Endo International Plc, are the latest companies with limited supply of some doses of generic extended-release Adderall, according to a website updated Monday by the University of Utah’s drug-information service, which tracks drug shortages.

Across the country, people with ADHD are having trouble filling prescriptions for the medicine, which is supposed to be taken daily. Going without the pills can make it difficult for people with ADHD to focus and complete everyday tasks. Demand for the drug is at an all-time high, according to Symphony Health.

Lannett spokesperson Robert Jaffe said the company is seeing spikes in demand for its 15-milligram extended-release pills because of market shortages. Endo didn’t immediately reply to an email seeking comment.

Nine companies supply branded and generic Adderall XR in the US, according to Erin Fox, senior pharmacy director at the University of Utah’s drug-information service. Other firms that face supply challenges for the drug are Amneal Pharmaceuticals Inc., Rhodes Pharmaceuticals LP (a subsidiary of Purdue Pharma LP), Novartis AG’s Sandoz unit, and Teva Pharmaceutical Industries Ltd.

Adderall has been in short supply at several points in recent years. The current issues started with a labor shortage at Teva, the nation’s leading seller of brand and generic instant-release Adderall.

The US Food and Drug Administration is not currently reporting a shortage of Adderall.

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