Emily Miller has an excellent series on this very topic.
It appears that as an out-of-stater to DC, pepper gas is generally legal for you to carry as an adult as long as you bought it outside of DC and you are not in a Federal Building or other prohibited location.
Here is the DC Pepper Spray Registration Form.
http://www.washingtontimes.com/blog/guns/2012/sep/25/miller-dcs-mace-control/
http://www.washingtontimes.com/blog/guns/2012/sep/27/miller-dcs-mace-control-part-2/
http://www.washingtontimes.com/blog/guns/2012/oct/3/miller-dc-mace-control-part-3/
http://www.washingtontimes.com/blog/guns/2012/oct/25/miller-dc-mace-control-part-4/
RealDefense 
At one time if you pepper sprayed a true psychotic individual that actually didn’t faze them and made them ? Appear stronger; is this still true? Have formulas changed overtime? I personally witness how chemical agents in a security setting did nothing to the individual being sprayed he remained enraged and worry about this on the street.
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Pepper spray is a less lethal option so it may be used in situations that would not merit the use of a firearm or it can be used in places in which the legal system frowns upon the right to self defense (such as New York City). Like any weapon, it is not an automatic guarantee of personal security.
It wouldn’t make a person stronger. Some people just don’t react to it at all. That is Murphy’s Law for you.
Stick with a reputable name brand like GuardPD.com or Fox Labs and you will have less likelihood of the pepper spray not creating enough pain to escape.
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Hello,
The blog is really very useful and informative!
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