Many pharmaceuticals were originally derived from plants, including:

• Aspirin
• Digoxin (used for congestive heart failure)
• Oral anticoagulants (blood thinners) 
• Some antiparasitics (used to kill parasites) (Fugh-Berman, 1997).

In addition, about 25 percent of all pharmaceutical drugs still include some plant-derived constituents.

So it is not surprising that botanical medicines often work in the body in ways that are similar to pharmaceutical drugs.

How do they work?

Like pharmaceutical drugs, botanical medicines adhere to principles of pharmacodynamics and pharmacokinetics. These are the scientific words for the study of how drugs interact with bodily systems.

• Pharmacodynamics is the study of drugs and their actions on living organisms. This science studies how drugs act on the body.
• Pharmacokinetics is the study of how the body digests, distributes, and excretes particular drugs. It looks at the time required for absorption, duration of action, distribution of drug in the body, and method of excretion. In other words, this science studies how the body acts on the drugs.

So, as with pharmaceuticals, scientists study how the active components in a particular botanical is absorbed, distributed, and metabolized in the body and then excreted. They also study the pharmacological activity—the effect the botanical has in the body. All this helps scientists understand the mechanism of action—where the drug goes in the body, what it does, and how that impacts the individual’s health.

Like many pharmaceutical drugs, there are botanical medicines for which the mechanism of action is unknown.

Examples

Here are the known or estimated mechanisms of action for two botanicals.

St. John’s wort extract, used to treat mild to medium depression, has been shown to block the reuptake of serotonin, as Prozac and other similar drugs do. Research with Prozac and other similar medicines has shown that increasing the levels of serotonin at the nerve synapse can minimize the symptoms of depression. St. John’s wort may also play a role in affecting mood by blocking catechol-O-methyltransferase, an enzyme that breaks down another class of neurotransmitters that are involved in mood change.

Saw palmetto is used to treat prostate enlargement (or benign prostatic hyperplasia), which is common in men older than 50. Although the exact mechanisms of action are unclear, many clinical studies have demonstrated that saw palmetto’s effectiveness is comparable to the two most common pharmaceutical treatments for prostate enlargement (finasteride, a 5-alpha-reductase inhibitor, and Doxazocin, an alpha-1 selective receptor antagonist). Research has led to several proposed mechanisms of action for saw palmetto extracts, including anti-inflammatory effects, anti-androgenic action (preventing the biologic effects of some male sex hormones), and antiproliferative (or chemotherapy) effects (Buck, 2004).

Why is synergy important?

Many botanicals are comprised of multiple active ingredients that act together (synergistically) to produce a response (Williamson, 2001). Thus, there may not be one active ingredient that accounts for all the observed effects.

This concept of synergy underlines much of the modern clinical use of botanical medicines, and there is an increasing body of evidence in support of its validity.

How do botanical medicines and pharmaceutical drugs differ?

While botanicals are like pharmaceuticals in many ways, there are important differences.

References

Ernst, E. (2007). Herbal medicines: Balancing benefits and risks. Novartis Foundation Symposium, 282, 154-67; discussion 167-72, 212-8.

Williamson, E.M. (2001). Synergy and other interactions in phytomedicines. Phytomedicine, 8, 401-409.

St. John's Wort

Barnes, J., Anderson, L.A., Phillipson, J.D. (2001). St John's wort: A review of its chemistry, pharmacology and clinical properties. Journal of Pharmacy and Pharmacology, 53(5), 583-600.

Butterweck, V. (2003). Mechanism of action of St John's wort in depression: What is known? CNS Drugs, 17(8), 539-62.

Kasper, S., Gastpar, M., Müller, W.E., Volz, H.P., Dienel, A., Kieser, M., Möller, H.J. (2007). Efficacy of St. John's wort extract WS(R) 5570 in acute treatment of mild depression: A re-analysis of data from controlled clinical trials. European Archives of Psychiatry and Clinical Neuroscience, Dec 14, 2007.

Medina, M.A., Martínez-Poveda, B., Amores-Sánchez, M.I., Quesada, A.R. (2006). Hyperforin: More than an antidepressant bioactive compound? Life Sciences, 79(2), 105-11.

Wurglics, M., Schubert-Zsilavecz, M. (2006). Hypericum perforatum: A 'modern' herbal antidepressant: Pharmacokinetics of active ingredients. Clinical Pharmacokinetics, 45(5), 449-468.

Saw Palmetto

Buck, A.C. (2004). Is there a scientific basis for the therapeutic effects of serenoa repens in benign prostatic hyperplasia? Mechanisms of action. Journal of Urology, 172(5 Pt 1), 1792-1799.

Fong, Y.K., Milani, S., Djavan, B. (2005). Role of phytotherapy in men with lower urinary tract symptoms. Current Opinion in Urology, 15(1), 45-48.

Wilt, T., Ishani, A., Mac Donald, R. (2002). Serenoa repens for benign prostatic hyperplasia. Cochrane Database of Systematic Reviews, 3, CD001423.

Expert contributor: Dennis McKenna, PhD

Date: April 2008

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