The answer to that is it depends on the country. A few examples of laws related to caffeine content for food and drinks include the following:
In the United States there is a limit of 65mg of caffeine per 12 liquid ounce in beverages. This may only be for carbonated beverages. (What we call coke here in the south and my northern friends like to call pop.) There is also a limit of 200mg in pills such as Vivrin. For more info on caffeine contents in drinks check outÂ High Caffeine Pop from 'Energy Drinks' Revealed. Also check Ask Erowid for more specifics.
Here is the FDA regulation text:
[Code of Federal Regulations]
[Title 21, Volume 3]
[Revised as of April 1, 2003]
From the U.S. Government Printing Office via GPO Access
TITLE 21--FOOD AND DRUGS
CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN
PART 182--SUBSTANCES GENERALLY RECOGNIZED AS SAFE--Table of Contents
Subpart B--Multiple Purpose GRAS Food Substances
Sec. 182.1180 Caffeine.
(a) Product. Caffeine.
(b) Tolerance. 0.02 percent.
(c) Limitations, restrictions, or explanation. This substance is
generally recognized as safe when used in cola-type beverages in
accordance with good manufacturing practice.
This text is available atÂ the GPO web site. Essentially what this means is that for a drink or food to fall within the FDA's guidelines 68 mgs per 12 oz is acceptable. Some drinks do have more. Most if not all energy drinks are legally classified as supplements. Supplements (vitamins and such) have a much lower oversight than food and drugs.
Natural caffeine levels are also exempt from these regulations so coffee based drinks may have more caffeine than the limit without being classified as a supplement.
Australia has a limit of Australia 145mg of caffeine per liter for non-energy drinks which they refer to as "formulated caffeinated beverage" for legal purposes. Formulated caffeinated beverages can contain up to 320 mg/L of caffeine but not less than 145 mg/L of caffeine.
In parts of Northern Thailand it is completely illegal. It was outlawed as a precursor to meth.
Legal limit on Caffeine with THC
In Ontario, the legal limit of caffeine in products containing THC is a maximum of 30 mg of caffeine and 10 mg of THC per dose. Any products containing both these drugs are restricted to this in a single serving (such as a can, or ground coffee).
On a relative basis, 30 mg caffeine is quite mild, while 10 mg of THC may be quite substantial for inexperienced users.
Consumers can take multiple doses, but products can not be legally manufactured or sold in Ontario with doses higher than this.
THC remains outright illegal in most of the world, including at the Federal level in the United States.