Doctors should limit the number of Effexor pills they prescribe patients to reduce the risk of overdose, the antidepressant's manufacturer and federal health officials said Wednesday.

There have been reports of deaths and serious injuries in patients who overdosed on Effexor, also called venlafaxine, predominantly when taken with alcohol and/or other drugs, Wyeth and the Food and Drug Administration said.

To limit the risk of overdose, doctors should prescribe the "smallest quantity of capsules consistent with good patient management," Wyeth wrote in a letter to doctors dated Oct. 17 and released Wednesday by the FDA.

Overdosing on any antidepressant can be fatal. But there may be a greater risk of deadly overdose associated with Effexor than with selective serotonin reuptake inhibitors — antidepressants like Prozac, Zoloft, Paxil and Lexapro, Wyeth said. The risk may be less than that with older antidepressants called tricyclics, it added.

Wyeth, based in Madison, N.J., said it was unclear whether the increased risk of deadly overdose can be attributed to Effexor or to the characteristics of patients treated with the drug.