Can a herbalist use herbs to decrease the side effects of pharmaceutical drugs?

Yes

There are many cases in which herbs strengthen the body’s response to prescription medications.  For example, herbs can reduce the amount of NSAIDS taken for rheumatoid arthritis thus reducing the risk of side effects. Herbs such as Aloe vera, may be used for patients on irradiation therapy to reduce their risk of throat ulceration, and Astragalus can help maintain a healthy white blood cell count.

Herbal medicine is an effective alternative for people who have allergic and other adverse reaction to drug treatment. Some people who have arthritis may develop chronic gastrointestinal problems from taking non steroidal anti-inflammatory drugs (NSAIDS). There is a wide range of herbs that relieve pain but without causing damage to the digestive tract or interfering with the NSAID treatment.

People with mild depression take powerful drugs, but with side effects such as weight gain, loss of appetite, fatigue, emotional extremes, and loss of libido. Herbal medicines such as Ginkgo have been researched and shown to prevent many of these side effects.