Analysis of Sonnet 118: Like as to make our appetite more keen

Like as to make our appetite more keen
With eager compounds we our palate urge,
As to prevent our maladies unseen,
We sicken to shun sickness when we purge.
Even so being full of your ne'er-cloying sweetness,
To bitter sauces did I frame my feeding;
And, sick of welfare, found a kind of meetness
To be diseased ere that there was true needing.
Thus policy in love t' anticipate
The ills that were not, grew to faults assured,
And brought to medicine a healthful state
Which, rank of goodness, would by ill be cured.
    But thence I learn and find the lesson true:
    Drugs poison him that so fell sick of you.