The most effective -- but slowest -- way for a drugmaker to increase a drug's sales is to expand its label so that it can treat a larger population. Teva Pharmaceuticals (NASDAQ:TEVA) did it quicker than usual yesterday. It announced that interim data from an ongoing trial testing its multiple sclerosis (MS) drug COPAXONE was good enough to submit to marketing authorities.

The trial tested the already approved drug in patients that have had a single clinical episode such as numbness, dizziness, or blurred vision, and an MRI suggestive of MS. Clinically defined MS requires two such attacks.

Patients taking COPAXONE instead of a placebo reduced their risk of getting a second attack by 44% and, of those who did experience a second event, it took more than twice as long for the second attack to occur.

Given that the drug has met its efficacy endpoint, the independent data-monitoring committee recommended that the control arm of the trial be stopped so that patients receiving placebo could be switched to COPAXONE.

Teva plans to use the data to expand the label in the U.S., Canada, and Europe to include patients that have had one attack suggestive of MS. The expanded label will be especially useful in Europe -- where COPAXONE is co-marketed with Sanofi-Aventis (NYSE:SNY) -- because the additional approvals will make it much easier for the duo to get reimbursements from government health-care agencies for the expanded patient population.

Probably the greatest benefit of the expanded label is that Teva will get patients onto its MS drug earlier in their disease progression, rather than the patient starting on another MS drug such as Biogen Idec's (NASDAQ:BIIB) AVONEX or Rebif from EMD Serono and Pfizer (NYSE:PFE). Since patients are likely to stick with a drug that's working, the expanded label should help Teva increase its market share in patients with clinically defined MS as well.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.