Great question, and important. I, too, am allergic to bee stings and carry an epi pen in my vehicles and when I hike, along with Benadryl.
Yes, Benadryl does cause drowsiness. In fact, diphenhydramine, it's chemical name, is the ingredient that is used in virtually all over-the- counter sleep aids (like Sominex or Nytol, and in Tylenol PM) because of it's drowsiness side-effects. And also because it is so safe.
There are several reasons that I carry Benadryl with me, and you should, too. It is the preferred antihistamine recommended by most allergists for insect sting sensitivity. Here's why:
1) It is the safest antihistamine on the market. If the attack is severe, the dose can be substantially increased without fear of overdose(ask you doc first, though)
2) The drug that is in your epi-pen is epinephrine. It is a vasoconstrictor that keeps your airway membrane tissues from swelling closed. It is a synthetic version of adrenaline, and like adrenaline, epinephrine is a fast acting, moderately strong stimulant. One could take a very large amount of Benadryl when using an epi-pen, and have zero-risk of drowsiness complications because the stimulant effects from the epinephrine not only counteract drowsiness, they are far stronger than any sleep inducing properties that Benadryl produces.
3) Benadryl is one of the faster-acting antihistamines, and is also very versatile in it's method of administration, important in severe, rapidly escalating anaphylaxis. You should carry the 25mg. gelatin-capsule form. The powder in the capsule form disperses rapidly, while the solid "caplet" takes longer to dissolve. Also, in severe cases, the sting site(s) can sometimes become extremely swollen and painful, due to a localized hyper-allergic reaction in addition to the bee venom. In this situation, if it is necessary to treat these sting site(s), an additional capsule of Benadryl can be opened up and the powder sprinkled directly on the skin at the site, and then moistened to a paste. The antihistamine is directly absorbed into the skin at the site, providing stronger local histamine blocking to the inflamed tissue. Additionally, Benadryl has (an unintentional beneficial side-effect) substantial anesthetic (pain-numbing) properties that begin to relieve local intense pain within about 30 seconds. Note: this additional topical dose of Benadryl does not need to be taken into consideration with regard to the original oral dose - it is absorbed locally and very little is absorbed into the bloodstream.
I'll bet this is more information than you were looking for, Kristina. Well, if you carry your epi-pen, and carry a packet of 25mg.Benadryl powder capsules, you'll be pretty safe. I was stung last year by 12 Africanized bees, and in the two minutes it took to walk home I was already choking and bright red all over. I got my pen and immediately swallowed three Benadryl, and called 911. I was already starting to stabilize by the time the paramedics arrived. Stuff works!
Hope this helped.
personal experience, discussions with my physicians, PDR