One part demulcent.
One part Aromatic.
One part Laxative. (optional, see below)
Two parts Active Herb.
 

Demulcents are substances taken internally for
their soothing or protective coating like properties,
to prevent irritation.
Some popular ones being;
Comfrey root
Flaxseed
Okra pods
Oatmeal
Irish moss
Licorice
Psyllium seed
Slippery Elm bark

Aromatics are substances with a fragrant smell,
which produce a peculiar sensation of warmth
and pungency.
Some popular ones being;
Anise seed
Caraway seed
Catnip
Cinnamon
Cloves
Coriander
Cumin
Eucalyptus
Fennel
Ginger
Mace (Nutmeg)
Mint (All)

Laxatives or Cathartics, eliminate poisons.
Psyllium seed, which is listed as a Demulcent,
in large enough quantities also has a laxative
effect. Others are;
Cascara bark
Castor Oil
Senna
Aloes
Jalap root
Blue flag root
Buckthorn bark

All of the above mentioned herbs are available through
any herb store or many mail order companies. Many cross
over from one category to the next. Catnip, which is an
Aromatic is also a relaxant, so it would not be combined
in stimulant preparations. Consult a good herb book from
the library or local book store for possible side effects
before compounding any herbal remedy.

The presence of the demulcent and
the aromatic are self explanatory.
If the potion is repulsive to the senses
one is not inclined to use it.
The laxative is an important part as
without proper evacuation of the
poisons, healing can not occur.
On the other hand this ingredient may be 
omitted in the case of treating bowel problems.
Doctrine of signatures and the Hot/Cold
principals can be employed for determining
the active principal.