According to the manufacturers of Liquid-Plumr, its drain opening products are safe to use on minor clogs in drains equipped with garbage disposals. The instructions advise to pour the product into the drain, let it sit for an hour, and then thoroughly flush the drain with hot running water.
Many professional plumbers advise against using agents like Liquid-Plumr on garbage disposals in kitchen drains as the chemicals in the product may harm pipes and fittings as well as parts of the disposal.
If the clog appears to be in the pipes rather than in the blades of the disposal, it may be safe to use a drain cleaning agent. However, if the clog has caused the disposal to freeze up and the motor cannot move the blades, a professional plumber is recommended to remedy the situation. Keep in mind that using drain opening chemicals may void the warranty on the garbage disposal.