www.needleplant.com

Compared to 真武汤，五苓散 treats a less severe form of dehydration.

Looking back on line 71 of 《伤寒论》:

“太阳病，发汗后，大汗出，胃中干，烦躁不得眠，欲得饮水者，少少与饮之，令胃气和则愈。” (Line 71a)

This line tells us that the patient has an exterior illness which is treated using perspiration. However, it is overdone, and causes vexation and insomnia. The reasoning is that over-perspiration has made the stomach (or the entire gastrointestinal system) dry. Treatment is by replenishing with fluids - SLOWLY - and once the stomach qi is harmonized, then the patient will recover.

The difference between this and the 太阳-type 真武汤 pattern is that the symptoms are not as severe. Hence, we need only replenish with fluids. Also the problem is still at the 脾胃 level. The 肾 is not damaged in this situation. And the dehydration only causes vexation. It does not really go to the point of causing low blood pressure and symptoms related to hypovolemic shock.

The second part of the line speaks of 五苓散:

“若脉浮，小便不利，微热消渴者，五苓散主之。” (line 71b)

Here we go. Only if commonsensical fluid replenishment doesn’t work do we opt for the next treatment protocol. To qualify, the patient not only needs to show exterior signs - see 脉浮 - there is also 五苓散’s characteristic symptoms: thirst and unsmooth passing of urine.

So it is used to treat dehydration - indicated by thirst. But what does the 小便不利 and the subsequent need for a diuretic mean? Just broadly, I understand it as a regulation of the body’s water metabolism, to bring it back to a normal state where you’re not thirsty, nor do you have problems urinating smoothly. That’s probably what 茯苓 and 桂枝 do as an herb-pair.

On when it gets worse do we consider 真武汤 to treat excessive dehydration.