Two experimental pills for multiple sclerosis proved effective in clinical trials, raising the possibility for the first time that oral treatments might become available alongside the more cumbersome injections and infusions used to treat MS today.

Some patients taking the drugs—made by Switzerland's Novartis AG and Germany's Merck KGaA—experienced adverse events that researchers said need to be carefully weighed against the drugs' benefits. The adverse events included herpes infections, a small number of cancer cases and...