You raise a provocative question. Weight-based dosing has been of increasing concern in medicine in recent years, particularly since so many people are now obese and may not get adequate treatment from dosages based on a "one size fits all" formula. Weight-based dosing has always been practiced in some fields of medicine – pediatrics, for example, where doctors never give the same amount of a drug to a three-month-old infant and a three-year-old toddler.
A cancer patient's bodyweight is also key to calculating correct chemotherapy dosages, but according to the American Society of Clinical Oncology (ASCO), until recently, 40 percent of obese cancer patients received limited chemo dosages not based on body weight. To remedy this, in 2012, ASCO issued new guidelines on chemotherapy dosages for obese patients, noting that clinical trials have clearly demonstrated that weight-based chemotherapy dosing "maximizes the effectiveness of the treatment" without increasing the risk of side effects. Optimal chemotherapy dosing is established through clinical trials and is generally calculated using a patient's body surface area along with weight and height.
In 2010, two Greek doctors made a case for considering adult body weight when prescribing antibiotics and antimicrobial drugs. Under current practices, they wrote, a 198-pound man with pneumonia would get the same antibiotic dosage as a 120-pound woman. They maintained that the obesity epidemic and the increasing prevalence of antibiotic resistance make it essential to individualize dosages based on patient size in order to optimize treatment. Changing the way antibiotics are prescribed would enhance their effectiveness and might also reduce the likelihood that microbes will develop resistance to the medications. One of the authors, Matthew E. Falagas, director of the Alfa Institute of Biomedical Sciences in Athens, Greece, and a professor of medicine at Tufts University School of Medicine in Boston, told the New York Times that the change would require drug companies to make more drugs available in liquid form or in several tablet sizes.
I discussed the issue of supplement dosage with Loren D. Israelsen, executive director of the United Natural Products Alliance (UNPA), a trade association of dietary supplement companies. Mr. Israelsen notes that "scaled dosing" is rarely seen on U.S. supplement labels and is more common in Europe. One reason for this, he explains, is that historically, the FDA did not permit supplement labels to carry this type of information. In fact, the agency regards any detailed dosing information as a drug claim. Another reason Mr. Israelsen cites is that the "the required knowledge to provide reliable weight-based dose recommendations does not exist in many cases, and so companies shy away for lack of technical knowledge."
He adds that "no doubt there are liability issues as well…the more specific the advice, the more responsible the company is for outcomes, especially if those outcomes are bad." Then there is the obesity epidemic. "When and how often would you revise dosage recommendations as the population gets bigger and fatter?" Mr. Israelsen asks, noting that we also need to consider the effect of obesity on metabolism of nutrients and other supplement ingredients.
So the answer to your question includes both regulatory concerns and technical challenges. The supplement industry is aware of the problem, and I hope we will see this issue addressed in the future.
Andrew Weil, M.D.