Shares of Guilford Pharmaceuticals ( GLFD) were among the worst-performing health-related stocks Thursday, falling 33.7% after the company said it would suspend its sedation drug trials because of numerous side effects.

Although its Aquavan drug met its primary endpoint of success of sedation in a phase III trial, a high level of side effects in the treatment group led it to voluntarily suspend enrollment of patients in its ongoing clinical trials while it examines dosing levels. The company plans to meet with the Food and Drug Administration during the next several weeks so that it can determine an optimal clinical plan that leads to approval and a desired label. "While these activities may modestly extend our time line for filing the NDA, we think it will best enhance the product's commercial opportunity," the company said. Shares traded down $1.19 to $2.34.

Pain Therapeutics ( PTIE) rose 1.2% after the company said a phase III trial showed that its oral opioid painkiller was less addictive than oxycodone. The company said that patients using its Oxytrex drug reported equal pain relief to patients using oxycodone but reported 20% less overall opioid-related side effects. According to Pain Therapeutics, the oxycodone market is about $2 billion in size, representing about 10 million prescriptions a year. "Will a broad swath of this market adopt a new drug that offers less physical dependence, less side-effects or lower dosing requirements? We believe so and that's why we're excited about our phase III results," the company said in a statement. The company plans to discuss an NDA strategy for Oxytrex with the FDA in late 2005 after it unblinds results from its second phase III trial. Shares traded up 7 cents to $5.94.

Shares of Natural Health Trends ( BHIP) fell 19.9% after the company posted fourth-quarter results that disappointed investors. The company posted a loss of $802,000, or 12 cents a share, on sales of $36.3 million. The one-analyst estimate called for the company to earn 14 cents a share. A year ago the company earned $1.1 million, or 19 cents a share, on sales of $22.6 million. Natural Health said the decline in earnings was due to higher commissions paid to distributors and higher selling, general and administrative expenses. Shares traded down $3.40 to $13.70.

Sonus Pharmaceuticals ( SNUS) fell 3.4% after the company posted a bigger fourth-quarter loss compared with a year ago. The drug developer posted a loss of $5.4 million, or 25 cents a share. A year ago the company posted a smaller loss of $2.6 million, or 15 cents a share. One analyst polled by Thomson First Call was expecting a loss of 18 cents in the latest quarter. Sonus ended the year with cash and marketable securities of $20.6 million. Shares traded down 11 cents to $3.09.

Other health care movers included Pfizer ( PFE - Get Report), up 13 cents to $26.17; Elan ( ELN), up 21 cents to $7.41; Johnson & Johnson ( JNJ - Get Report), down 11 cents to $68.09; Bristol-Myers Squibb ( BMY), down 30 cents to $25.02; Merck ( MRK), down 19 cents to $31.87; Amgen ( AMGN), up 12 cents to $58.98; Genentech ( DNA), up 69 cents to $58.75; Biogen Idec ( BIIB), up 70 cents to $38.80; and Schering-Plough ( SGP), down 30 cents to $18.02.