I've used slippery elm tea to soothe irritated intestines after suffering from gastritis and digesting massive amounts of acid. It's used orally for sore throats because it soothes mucus membranes, so I decided to try it rectally and it worked the same and really helped to cool things down and lubricate and protect the rectal tissue.
I have not used catnip as an enema; just as s drug to keep my cats from acting like cats some nights - my little stoners. Catnip, valerian and passionflower have calming effects on the body.
I've used peppermint tea afer coffee enemas, which I take for headaches or for a general all over sluggishness. I don't use it for any benefit other than to feel the cool soothing effect of it and to flush out any coffee. I hate the smell and taste of coffee, so a peppermint enema after a coffee enema is pretty much the same as popping a mint after you have a cup of coffee to get rid of coffee breath.
I have used gingko tea to help alleviate mood swings due to mental and physical exhaustion. When you're tired and/or stressed, your blood vessels constrict and your brain does not get the oxygen it needs to perform properly. Gingko is also used to relieve high blood pressure. It works by dilating and therefore improving circulation to the extremeties and brain. That's the reason it is used by patients who have suffered strokes and mild neurological disorders. You've probably heard Alex Trebek advertise it Ginkoba (gingko biloba) capsules on tv. If your blood pressure tends to be low or on the low side of normal, use gingko wisely and sparingly until you know how it will affect your body.
I've used pau d'arco to treat an overgrowth of "bad bacteria" after a series of harsh soapy enemas washed out the "good bacteria." Pau D'arco is also used orally to treat thrush and vaginally to treat yeast infections. It is anti-fungal, anti-viral and anti-bacterial, so it's great stuff to have on hand during the winter (or any time of the year). I have never noticed any side effects from pau d'arco, but that doesn't mean there aren't any. It us a tree bark and tastes like Irish Whiskey, so it does not taste as bad as some herbs, if you need to drink it. I add a few drops of stevia to it and it's tastes fine.
There are a few herbs that I'd be interested in learning more about. Lobelia has been used to wean people off of tobacco cigarettes. However, a few years ago, there was a study about possible liver damage from using lobelia. But I don't know what to think about the research as scientists generally test lab animals with massive amounts of something and not the normal human dose. I've talked with a few people who received lobelia enemas as children and they suffered no ill effects from it, neither then nor now. I'd like to hear if anyone has used it to treat their tobacco addiction, how effective it was and what results they had.
Another herb I'd like to look into is damiana. It's a female arousal stimulant herb and I can testify that it works when taken orally. I subjected myself to a personal study of it several years ago and much to my surprise, it was very effective. I rarely use it, but whenever I'm feeling sexy and in the mood for some fun and either aren't quite there or want to make it eve better, I'll drink a 20 to 30 drops of damiana extract. Damiana can also be smoked, but I've never done that.
As with any medication, it can have a stronger effect on your body taken rectally than it may if taken orally as the colon is rich with blood vessels and the herb bypasses the stomach and travels directly and quickly into the bloodstream. Don't think that because it's "just an herb" that it isn't as dangerous as medication. The heart medication Digitalis is a chemical version of foxglove, which can be deadly if used incorrectly. Aspirin is the chemical form of white willow bark, so anyone with an allergy or sensitivity to aspirin should not use white willow bark. There are many others, but I don't have my reference books handy and am too tired to think too hard this morning.
With any herb, research it before you use it. Michael Cunningham, Kathy Keville, Rosemary Gladstar, James A. Duke and Susan Weed are a few of my favorite herbalists/authors. I highly recommend them and the magazines Herbs for Health, Body + Soul, Natural Health, and Alternative Medicine.
Good luck.